1. Field of the Invention
The present invention relates to a technology for detecting a dust near a scanning position of an original when reading an image of the original to generate image data.
2. Description of the Related Art
Some of image reading devices used in image processing apparatuses such as multifunctional products (MFPs) can scan both surfaces of an original at the same time (see, for example, Japanese Patent Application Laid-open No. 2007-82033). FIG. 25 is a schematic diagram of a conventional image reading device disclosed in Japanese Patent Application Laid-open No. 2007-82033. The conventional image reading device includes an automatic document feeder (ADF) 101 on the upper side and an optical reading unit 102 on the lower side.
The ADF 101 includes a feeder tray 151 on which originals are stacked, a contact image sensor (CIS) 135 that scans an image from the original and converts the image to an electrical signal, a discharge tray 152 onto which the original is discharged after the scanning, and a conveyer mechanism that conveys the original from the feeder tray 151 to the discharge tray 152 passing on the CIS 135. The conveyer mechanism includes a pick-up roller 153, a conveyer drum 154, and a discharge roller 157. The CIS 135 includes, although not shown, a light source such as a light-emitting diode (LED), a SELFOC lens array, an image sensor element, an analog-to-digital (A/D) converter circuit, and a digital processing circuit. A white reference roller 137 is arranged in opposite to the CIS 135.
The optical reading unit 102 includes a first carriage 174 including a xenon lamp 160 and a mirror, a second carriage 176 including two mirrors, a lens 178, a charge coupled device (CCD) sensor 161, a sensor board unit (SBU), and a driving unit (not shown) that drives the first carriage 174 and the second carriage 176. The SBU includes a signal processing unit that processes a signal from the CCD sensor 161. An exposure glass 180 and a scanning aperture 181 are provided on the upper surface of the optical reading unit 102. A white reference plate 182 is positioned over the end of the exposure glass 180 that is close to the scanning aperture 181.
The image reading device has a duplex scanning mode in which both surfaces of the original are scanned with the ADF 101 conveying the original. In the duplex scanning mode, the original is conveyed from the feeder tray 151 by the conveyer mechanism with the first carriage 174 being fixed below the scanning aperture 181. The front surface of the original is scanned when the original passes over the scanning aperture 181, and the rear surface of the original is scanned when the original passes on the CIS 135. Thus, the image reading device scans the both surfaces of the original with a single convey operation.
FIG. 26 is a block diagram of a conventional image processing apparatus including an image reading device such as the one shown in FIG. 25, although it is not described in a literature. The conventional image processing apparatus writes image data obtained from the front surface and the rear surface of the original to a memory. After that, the conventional image processing apparatus reads the image data of the front surface from the memory, processed the image data, and sends it to a controller, and then reads the image data of the rear surface from the memory, processed the image data, and sends it to the controller.
A reading unit 1, which optically reads the front surface of the original, focuses a reflection light generated by reflection of a lamp light on the original on a CCD as a light-receiving element. The light-receiving element is incorporated in a front surface sensor board unit (SBU_U) 2. The light-receiving element converts the image signal into an electric signal. The front surface sensor board unit 2 converts the electric signal into a digital signal, and sends it to a buffer memory controller (BMCTL) 51.
Similarly, a reading unit 3, which optically reads the rear surface of the original, obtains the image data by scanning the rear surface with a CIS, and thus the image data is converted to an electric signal. A rear surface sensor board unit (SBU_D) 4 converts the electric signal into a digital signal, and sends it to the buffer memory controller 51.
Upon receiving the front image data from the front surface sensor board unit 2 and the rear image data from the rear surface sensor board unit 4, the buffer memory controller 51 temporarily stores the image data in a buffer memory (BMEM) 6. After that, the front image data is sent from the buffer memory 6 to an image processing processor (IPP) 7. The image processing processor 7 makes up for degradation of signals caused at the scanning, and sends it to an image-data control unit (CDIC) 8.
The image-data control unit 8 controls transmission of image data between functional devices and data buses. More particularly, the image-data control unit 8 controls transmission of image data between the front surface sensor board unit 2, the rear surface sensor board unit 4, a parallel bus 11, and the image processing processor 7, and transmission of image data between a system controller 13 and a process controller 22. The system controller 13 is, for example, a central processing unit (CPU), which controls the image processing apparatus.
Upon receiving the front image data from the image processing processor 7, the image-data control unit 8 sends the front image data to an image-memory-access control unit (IMAC) 12 via the parallel bus 11. Under control of the system controller 13, the image-memory-access control unit 12 controls access to a memory (MEM) 15 with the image data, load of print data for an external personal computer (PC) that is connected to a network 16, and compression/decompression of the image data for efficient memory usage.
The image-memory-access control unit 12 compresses the image data, and writes the compressed image data to the memory 15. The image data is read from the memory 15 as appropriately. After the front image data is written in the memory 15, the buffer memory controller 51 reads the rear image data from the buffer memory 6. The rear image data is written in the memory 15 after processed in the same manner as the front image data is processed. The image-memory-access control unit 12 reads the image data from the memory 15, decompresses the image data, and sends the decompressed image data to the image-data control unit 8 via the parallel bus 11.
After that, the image-data control unit 8 sends the image data to the image processing processor 7. The image processing processor 7 performs an image quality processing, and sends the processed image data to a video-data control unit (VDC) 9. The video-data control unit 9 performs pulse control based on the received image data, and thereby an image forming unit 10 forms an image on a recording medium as a reproduced image.
In the flow of image data, the functions as the MFP are implemented under control of the parallel bus 11 and the image-data control unit 8. When a plurality of jobs, for example, copying, scanning, and printing are executed in parallel, the system controller 13 and the process controller 22 control assignment of a right to use the reading units 1 and 3, the image forming unit 10, and the parallel bus 11 to the jobs. The process controller 22 controls the flow of image data. The image-memory-access control unit 12 controls the image processing apparatus, and controls activation of the resources. The user selects a desired function of the MFP and adjusts detailed settings for copying or scanning by manipulating an operation panel 17. The system controller 13 and the process controller 22 communicate with each other via the parallel bus 11, the image-data control unit 8, and a serial bus 21. The image-data control unit 8 performs data format conversion between parallel data and serial data so that the image data can be transferred between the parallel bus 11 and the serial bus 21.
When the front surface and the rear surface are scanned, the image processing processor 7 receives the front image data from the front surface sensor board unit 2 and the rear image data from the rear surface sensor board unit 4, and performs the image quality processing. Upon receiving the processed image data from the image-data control unit 8 via the parallel bus 11, the image-memory-access control unit 12 stores the processed image data in the memory 15 or a hard disk drive (HDD) 14. The image-memory-access control unit 12 reads the front image data and the rear image data from the memory 15 or the HDD 14, and sends them to the PC via the network 16 as appropriately.
FIG. 27 is a block diagram of the buffer memory controller 51. In the buffer memory controller 51, when the front image data is received from the front surface sensor board unit 2, the front image data is written in the buffer memory 6 via a first-image-input control unit 511, a first-memory-write control unit 512, a memory-access arbitration unit 513, and a memory interface (I/F) control unit 514. On the other hand, when the rear image data is received from the rear surface sensor board unit 4, the rear image data is written in the buffer memory 6 via a second-image-input control unit 515, a second-memory-write control unit 516, the memory-access arbitration unit 513, and the memory I/F control unit 514.
The front image data and the rear image data are sent from the buffer memory 6 to the image processing processor 7 via the memory I/F control unit 514, the memory-access arbitration unit 513, and a memory-read control unit 517.
FIG. 28 is a block diagram of the image processing processor 7. Upon receiving the image data from the buffer memory controller 51, an input I/F 71 sends the image data to a scanned-image processing unit 72. The scanned-image processing unit 72 makes up for degradation of the image quality of the image data that has been just scanned (hereinafter, “scanned data”), by using various corrections including shading correction, gamma correction, modulation transfer function (MTF) correction, dust detection, and dust correction. The scanned-image processing unit 72 sends the corrected image data to the image-data control unit 8 via an output I/F 73.
Before the image is formed on the recording medium, an image-quality processing unit 75 receives the image data from the image-data control unit 8 via an input I/F 74, and adjusts gradation of the image data by using approximate approaches. More particularly, the image-quality processing unit 75 performs density adjustment, dithering, and random dithering. The processed image data is sent to the video-data control unit 9 via an output I/F 76. If the corrected image data that has been processed by the scanned-image processing unit 72 is stored in the memory 15, various image data with different qualities are created from the single corrected image data, and the user can check the various image data with different qualities. For example, various images that give different impressions can be formed by changing density or the number of lines of dithering matrix. The image-quality processing unit 75 can create various image data from the corrected image data stored in the memory 15 instead of from the scanned data. If the reading unit is a stand-alone scanner, the image processing processor 7 corrects quality defects and adjusts the gradation at the same time, and sends the processed image data to the image-data control unit 8. A command control unit 77 switches the processes, changes order of the processes, or the like.
FIG. 29 is a block diagram of the image-data control unit 8. An image-data input control unit 81 receives the image data processed by the image processing processor 7. A data compressing unit 82 compresses the received image data, thereby creating compressed data that can be transferred in a shorter time via the parallel bus 11. The compressed data is sent to the parallel bus 11 via a parallel data I/F 84. On the other hand, upon receiving compressed image data from the parallel bus 11 via the parallel data I/F 84, a data decompressing unit 85 decompresses the compressed image data. The decompressed image data is sent to the image processing processor 7 via an image-data output control unit 86.
The image-data control unit 8 enables communication between the system controller 13 and the process controller 22. Upon receiving parallel data from the system controller 13 via the parallel bus 11, the image-data control unit 8 converts the parallel data to serial data, and sends the serial data to the process controller 22. Upon receiving serial data from the process controller 22 via the serial bus 21, the image-data control unit 8 converts the serial data to parallel data, and sends the parallel data to the system controller 13.
FIG. 30 is a block diagram of the video-data control unit 9. Upon receiving the image data from the image processing processor 7, the video-data control unit 9 processes the image data based on properties of the image forming unit 10 (dot re-arrangement process by an edge smoothing unit 91, pulse control by a pulse control unit 92 for creating dots of the image data, and etc.) and sends the processed image data to the image forming unit 10. The video-data control unit 9 can perform, in addition to image-data processing, format conversion by using a data converting unit 94. Upon receiving parallel data from a parallel data I/F 93, the data converting unit 94 converts the parallel data to serial data. On the other hand, upon receiving serial data from a serial data I/F 95, the data converting unit 94 converts the serial data to parallel data. With this configuration, the video-data control unit 9 solely enables communication between the system controller 13 and the process controller 22.
FIG. 31 is a block diagram of the image-memory-access control unit 12. The image-memory-access control unit 12 writes/reads the image data to/from the memory 15. Moreover, the image-memory-access control unit 12 receives code data from, for example, an external PC, and loads the code data as the image data.
A parallel data I/F 121 is connected to the parallel bus 11 and controls transmission/reception of the image data. Upon receiving the code data from the external PC via the network 16, the image-memory-access control unit 12 stores the code data in a local area of a line buffer 123. Upon receiving a load command from the system controller 13 via a system controller I/F 124, a video control unit 125 loads the code data stored in the line buffer 123 as the image data.
The loaded image data or the image data received from the parallel bus 11 via the parallel data I/F 121 is stored in the memory 15. More particularly, a data converting unit 122 selects the image data to be stored, and a data compressing unit 126 secondarily compresses the selected image data for efficient usage of the memory 15. A memory-access control unit 127 stores the compressed image data in the memory 15, managing an address in the memory 15.
The memory-access control unit 127 reads target image data from the memory 15 by an address of the target image data. The image data is then decompressed by a data decompressing unit 128. If the decompressed image data is to be sent to the parallel bus 11, the data converting unit 122 converts the image data to the parallel data, and sends the parallel data via the parallel data I/F 121.
FIG. 32 depicts image paths IP1, IP2, and IP3 along which the scanned image data of both surfaces are transferred. Along the image path IP1, the front image data is sent to the buffer memory controller 51 via the reading unit 1 and the front surface sensor board unit 2, and is stored in the buffer memory 6. Along the image path IP2, the rear image data is sent to the buffer memory controller 51 via the reading unit 3 and the rear surface sensor board unit 4, and is stored in the buffer memory 6.
After that, along the image path IP3, the front image data and the rear image data are sent from the buffer memory 6 to the image-memory-access control unit 12 via the buffer memory controller 51, the image processing processor 7, the image-data control unit 8, and the parallel bus 11, and is stored in the memory 15. The front image data and the rear image data are then stored in the HDD 14 as appropriately.
FIG. 33 is a timing chart illustrating timing when the image data is transferred. In the timing chart, signals attached with U2B_ at their heads are indicative of signals that are sent from the front surface sensor board unit 2 to the buffer memory controller 51; signals attached with D2B_ at their heads are indicative of signals that are sent from the rear surface sensor board unit 4 to the buffer memory controller 51; and signals attached with B2I_ at their heads are indicative of signals that are from the buffer memory controller 51 to the image processing processor 7. Signals named FGATEB are frame gate signals; signals named LSYNCB are line synchronization signals. Signals named RD are signals of red image data; signals named GD are signals of green image data; and signals named BD are signals of blue image data. When the frame gate signal is low, a line synchronization signal and the image data signals (i.e., RD, GD, and BD) are active. Pieces of the image data, each corresponding to one line, are sent one by one in synchronization with the line synchronization signal. The image data is 8-bit pixels.
As shown in FIG. 25, the CIS 135 as the image sensor for scanning the rear surface is arranged downstream of the scanning aperture 181 through which the front surface is scanned. This is because the buffer memory controller 51 receives the rear image data a little after receiving of the front image data as shown in FIG. 33. The rear image data is sent from the buffer memory controller 51 to the image processing processor 7 in serial, following the front image data.
FIG. 34 is an enlarged view of the CIS 135 and the white reference roller 137 shown in FIG. 25. The original is conveyed between the CIS 135 and the white reference roller 137. FIG. 35 is a schematic diagram of the original and the scanned data that is obtained by using the CIS 135 shown in FIG. 34. An image A is the original, and an image B is the scanned data. The CIS 135 scans the original, one line after another. Those lines are arranged in the sub-scanning direction Y, i.e., a direction in which the original shown in FIG. 34 is fed. Pixels of each line are arranged in the main-scanning direction X. The reading unit 3 scans the white reference roller 137 before scanning the original, thereby obtaining the white reference data that is used for correcting the scanned image data. In other words, the white reference roller 137 is used for generating the white reference data, while conveying the original. A line length L of the white reference data is equal to a circumference length of the white reference roller 137 (i.e., diameter φ×circle ratio π).
FIG. 36 depicts the CIS 135 with a dust on its scanning surface; FIG. 37 is a schematic diagram of the scanned data that is obtained from the white reference roller 137 and the scanned data that is obtained from the original by using the CIS 135 shown in FIG. 36. The image A is the original, the image B is the scanned data, and an image C is the corrected image data. As show in the image B, undesired lines are formed on both the white reference data and the image data because the dust is on the CIS 135. To obtain image data with no undesired line, the dust detection is performed before scanning of the original. If a dust is detected, a message for causing the user to remove the dust is displayed on the operation panel 17.
It is possible to remove the undesired lines from the white reference data and the image data by identifying a position of the dust and replacing correction data with an area including the undesired line by using the dust correction. A method of the dust correction is not explained in detail because the dust correction is a widely-known technique. As shown in the image C, the image data is corrected to approximately dustless data.
FIG. 38 depicts the white reference roller 137 with a dust on its circumference; FIG. 39 is a schematic diagram of the scanned data that is obtained from the original and the scanned data that is obtained from the white reference roller 137 shown in FIG. 38. The image A is the original, and the image B is the scanned data. Because the dust is on the circumference of the white reference roller 137 as shown in FIG. 38, an interrupted line is formed on the white reference data as shown the image B of FIG. 39. The interrupted line has a predetermine cycle corresponding to the circumference length of the CIS 135. No undesired line is formed on the image data because no dust is on the CIS 135. However, there is possibility of miss-correction because the white reference data with the undesired line is used.
A position of the dust, on the CIS 135 or on the white reference roller 137, can be identified by analyzing the white reference data. If the continuous line shown in the image B of FIG. 37 is formed on the white reference data, the dust is on the CIS 135. On the other hand, if the interrupted line shown in the image B of FIG. 39 is formed on the white reference data, the dust is on the white reference roller 137.
FIG. 40 is a schematic diagram for explaining signals that are sent from the rear surface sensor board unit 4 to the image processing processor 7 via the buffer memory controller 51. FIG. 41 is a timing chart of the signals shown in FIG. 40, illustrating timing when the white reference data and the image data as shown in, for example, the image B of FIG. 39 are sent. There are a dust detection period, a pause period, and an image-data input period.
FIG. 42 is a flowchart of a single-surface storing process in which the buffer memory controller 51 stores the white reference data and the image data in the buffer memory 6.
The buffer memory controller 51 determines whether a dust detection mode is ON (Step S51). If the dust detection mode is ON (Yes at Step S51), the buffer memory controller 51 stores the dust detection data (i.e., white reference data) in the buffer memory 6 in synchronized with the line synchronization signal (i.e., D2B_LSYNCB signal) (Step S53) during a period between when a D2B_FGATEB signal is asserted (Yes at Step S52) and when the D2B_FGATEB signal is negated (Yes at Step S54). The user sets ON/OFF of the dust detection mode by manipulating the operation panel 17. Settings of the dust detection mode are stored in a register (not shown) incorporated in the buffer memory controller 51. After the buffer memory controller 51 finishes storing of the dust detection data (Step S55), the buffer memory controller 51 stores the image data in the buffer memory 6 in synchronized with the D2B_LSYNCB signal (Step S57) during a period between when the D2B_FGATEB signal is asserted (Yes at Step S56) and when the D2B_FGATEB signal is negated (Yes at Step S58). If the dust detection mode is OFF (No at Step S51), the buffer memory controller 51 stores only the image data in the buffer memory 6. In this manner, the buffer memory controller 51 separately stores the white reference data at Step S53 (see (7) of FIG. 42) and the image data at Step S57 (see (8)), which makes the system control complicated.
FIG. 43 is a flowchart of a single-surface reading process of reading the white reference data and the image data from the buffer memory 6. The white reference data for the front image data is obtained by scanning the white reference plate 182, and the white reference data for the rear image data is obtained by scanning the white reference roller 137.
The buffer memory controller 51 activates reading operation from the buffer memory 6 (Step S60) and determines whether the dust detection mode is ON (Step S61). If the dust detection mode is ON (Yes at Step S61), the buffer memory controller 51 asserts the D2B_FGATEB signal (Step S62) and sends lines of the dust detection data (equivalent to the sub-scanning length of the white reference plate 182 or the white reference roller 137) to the image processing processor 7 in synchronized with the D2B_LSYNCB signal (Step S63). When the buffer memory controller 51 finishes sending all lines of the dust detection data, (Yes at Step S64), the buffer memory controller 51 negates the D2B_FGATEB signal (Step S65).
After that, the buffer memory controller 51 is on standby for a predetermined period (Step S66). When the predetermined period has passed, the buffer memory controller 51 asserts a B2I_FGATEB signal for sending the image data (Step S67), and sends received lines of the image data to the image processing processor 7 in synchronized with the line synchronization signal (i.e., B2I_LSYNCB signal) (Step S68). When the buffer memory controller 51 finishes sending of all lines of the image data (Yes at Step S69), the buffer memory controller 51 negates the B2I_FGATEB signal (Step S70).
In this manner, the buffer memory controller 51 separately sends the white reference data at Steps S63 and S64 (see (9) of FIG. 43) and the image data at Steps S68 and S69 (see (10)), which makes the system control complicated.
FIG. 44 is a flowchart of a both-surface reading process of reading the white reference data and the image data from the buffer memory 6.
The buffer memory controller 51 activates reading operation from the buffer memory 6 (Step S71) and determines whether the dust detection mode for the front surface is ON (Step S72). If the dust detection mode for the front surface is ON (Yes at Step S72), the buffer memory controller 51 reads the white reference data for the front surface and the front image data in the same manner as in Steps S62 to S70 (Steps S73 to S81). After that, the buffer memory controller 51 determines whether the dust detection mode for the rear surface is ON (Step S82). If the dust detection mode for the rear surface is ON (Yes at Step S82), the buffer memory controller 51 reads the white reference data for the rear surface and the rear image data in the same manner as in Steps S73 to S81 (Steps S83 to S91).
In this manner, the buffer memory controller 51 separately sends the white reference data for the front surface at Steps S74 and S75 (see (11) of FIG. 44), the front image data at Steps S79 and S80 (see (12)), the white reference data for the rear surface at Steps S84 and S85 (see (13)), and the rear image data at Steps S89 and S90 (see (14)), which makes the system control more complicated.
FIG. 45A is a timing chart when the dust detection is performed before scanning of each page of the original. In the example shown in FIG. 45A, even if a dust gets attached during scanning of a certain page, the dust is detected before scanning the next page. However, the scanning speed is low. FIG. 45B is a timing chart when the dust detection is performed only before scanning of the top page of the original. In the example shown in FIG. 45B, the scanning speed is higher than the example shown in FIG. 45B. However, if a dust gets attached during scanning of a certain page, an undesired line may be formed on image data corresponding to the next page and subsequent pages.
FIG. 46 is a schematic diagram for explaining the required capacity of the buffer memory 6 for storing therein the dust detection data (white reference data) and the image data. If the original is an A3 size (297 mm×420 mm main-scanning direction×sub-scanning direction) or a double letter size (279.4 mm×431.8 mm main-scanning direction×sub-scanning direction), the scanning area is set to 320 mm×431.8 mm, taking it into consideration that a margin for the correction data is added in the main-scanning direction and an actual size being of the recording medium is larger than the A3 size. If the diameter φ of the white reference roller 137 is 30 mm, then the circumference length is 94.2 mm. It is assumed that a full-color image is scanned as the original and both surfaces of the original are stored with a scanning resolution of 600 dots per inch (dpi) with 8-bit pixels. The main-scanning length of 320 mm is equal to 7205 pixels. The upper address should be in a single line because data is stored in the buffer memory 6 as a dynamic random access memory (DRAM) by using burst transfer. Assume that one line is 8 kilobytes (8 kilobytes per line, because of each pixel being 8 bit). In other words, the scanning conditions are as follows:
(1) Scanning area (main-scanning length × sub-scanning length)Original:320 mm × 431.8 mmWhite reference roller 137:320 mm × 94.2 mm(2) Number of pixels × number of linesOriginal:8 kilobytes × 10200White reference roller 137:8 kilobytes × 2225(3) Required memory capacityOriginal: 79.7 megabytes × 3 (RGB) = 239.1 megabytes ≈ 240 megabytesWhite reference data: 17.4 megabytes × 3 (RGB) =  52.2 megabytes ≈ 53 megabytes
In this manner, the buffer memory 6 needs the capacity of 586 megabytes as shown in FIG. 46. The memory devices widely available in the DRAM market are 512-megabit memories, 768-megabit memories, and 1-gigabit memories. Therefore, twelve 512-megabit memories or six 1-gigabit memories are needed to obtain the capacity of 586 megabytes. Those memories cost roughly several tens of thousands yen.
FIG. 47 is a block diagram of another conventional image processing apparatus, although it is not described in a literature. The conventional image processing apparatus shown in FIG. 47 includes a dust detection unit (GOMI_U) 19 that is connected to both the front surface sensor board unit 2 and the buffer memory controller 51, and a dust detection unit (GOMI_D) 20 that is connected to both the rear surface sensor board unit 4 and the buffer memory controller 51. The dust detection is performed by the dust detection units 19 and 20, instead of the image processing processor 7, before data is stored in the buffer memory 6.
FIG. 48 is a block diagram of the dust detection units 19 and 20. The dust detection units 19 and 20 perform the dust detection and the dust correction. An input I/F 191 receives the front image data from the front surface sensor board unit 2, and sends the received front image data to a dust detection/correction unit 192. An input I/F 201 receives the rear image data from the rear surface sensor board unit 4, and sends the received rear image data to a dust detection/correction unit 202. The dust detection/correction units 192 and 202 perform the dust detection and the dust correction for the received image data. After that, the front image data and the rear image data are sent to the buffer memory controller 51 via output I/Fs 193 and 203, respectively.
FIG. 49 depicts signals that are sent from the front surface sensor board unit 2 to the dust detection unit 19, and signals that are sent from the dust detection unit 19 to the buffer memory controller 51. Signals that are sent from the rear surface sensor board unit 4 to the dust detection unit 20 and signals that are sent from the dust detection unit 20 to the buffer memory controller 51 are similar to those shown in FIG. 49.
FIG. 50 is a timing chart illustrating timing when the signals are sent from the front surface sensor board unit 2 to the dust detection unit 19. Those signals are active during the dust detection period and the image-data input period. FIG. 51 is a timing chart illustrating timing when the signals are sent from the dust detection unit 19 to the buffer memory controller 51. As shown in FIGS. 50 and 51, it is unnecessary to store the dust detection data in the buffer memory 6 because the dust detection unit 19 performs the dust detection. Thus, only the image data is stored in the buffer memory 6.
FIG. 52 is a schematic diagram for explaining the required capacity of the buffer memory 6 if the dust detection units 19 and 20 are in operation. Because the dust detection data is not stored in the buffer memory 6, the total required capacity is decreased to 480 megabytes. In other words, if the buffer memory 6 is 512-megabit memories, the number of memories decreases from 12 to eight. If the buffer memory 6 is 1-gigabit memories, the number of memories decreases from six to four. However, costs for the dust detection units 19 and 20 that can be an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA) are added in the total costs.
Thus, the conventional image processing apparatus needs memories with high capacity, which makes the cost increase. Moreover, because it is necessary to transfer a large amount of dust detection data, it is difficult to shorten intervals between scanning of original. In contrast, in the conventional image processing apparatus, the required memory capacity decreases with an advantage of the dust detection units 19 and 20. However, adding of the dust detection units 19 and 20 results in the cost increase.